About 500 people were evacuated from a terminal at Los Angeles International Airport on Monday when an alarm went off inside an unattended bag, officials said.

The alarm came from a megaphone packed inside the bag, which was discovered inside lobby of the Tom Bradley International Terminal around 11 a.m., prompting an immediate evacuation, said LAX spokesman Albert Rodriguez.

Authorities determined that the bag was harmless and airline passengers were allowed back into the terminal about 50 minutes later, Rodriguez said. No flights were affected by the incident.